In an electrophotographic image forming apparatus, a developing method is employed in which for example, a surface of an electrostatic latent image carrier of a photoreceptor or the like is charged, the charged region is exposed according to image information to form an electrostatic latent image, and the electrostatic latent image is developed to be visualized (developed). Such a developing method includes a single-component developing system which uses only a toner as a developer, without using a carrier.
A main configuration of the developing device includes a developing roller for developing a toner on a photoreceptor, a supply roller for performing supply of a toner to the developing roller and scraping (peeling) of a toner from the developing roller, and a toner layer regulation blade for regulating the toner supplied from the supply roller to the developing roller to a predetermined amount.
In the developing device as described above, the stability is regarded as the biggest challenge. Therefore, it is important to detect variation in a charging amount due to change of a toner, toner peeling failure due to surface hardening of the supply roller and the like.
For example, Japanese Laid-Open Patent Publication No. 9-197943 describes a developing device (process cartridge) which measures a current flowing between a developing roller and a conductive supply roller in contact with the developing roller, thereby detecting deterioration in the supply roller so as to issue a warning to a user before occurrence of image failure.
In the developing device described in the above Japanese Laid-Open Patent Publication No. 9-197943, it is focused on that there is interrelation between aggravation of adhesiveness between the supply roller and the developing roller caused by occurrence of surface wear of the supply roller and fraying of a foamed cell in the case of performing massive amount of printing, and a value of a current flowing between the supply roller and the developing roller. That is, when the adhesiveness between the supply roller and the developing roller gets worse, the flowing current reduces, which therefore is described to be usable to detect deterioration in the supply roller.
However, the value of the current flowing between the developing roller and the supply roller is influenced by two values of a toner charging amount of the developing roller and a toner peeled amount by the supply roller. When only the value of the current flowing between the developing roller and the supply roller is measured, it is indistinguishable whether variation in the values is due to a change in the toner charging amount of the developing roller or a change in the toner peeled amount of the supply roller. Accordingly, there is a possibility to be judged, for example, even when there is actually the change in the toner charging amount, that the toner peeled amount is changed so as to cause an erroneous operation such as emitting an exchange signal of the supply roller, thereby posing a problem that process control and deterioration detection of the supply roller and the like are not able to be performed appropriately.